Recent studies have established that seven congenic pigment mutations in the mouse cause prolonged bleeding. Their characteristics closely resemble those found in human platelet storage pool diseases (SPD) including Chediak-Higashi Syndrome and Hermansky-Pudlak Syndrome. The long term goals of this research include the identification of the primary biochemical abnormalities in these mutants. This in turn will enable therapeutic approaches at the molecular level. Identification of the altered regulatory steps in the mutants will provide valuable information about steps in normal megakaryocytopoiesis and platelet granule production. Five congenic mutations, in addition to the above seven, have recently been found to cause prolonged bleeding and their mechanism of action appears different from that of the original seven. A long term goal of this research is the further characterization of these mutants, especially to determine if they are appropriate animal models for other human bleeding diseases. The specific aims of this research are: a) To determine the primary biochemical abnormality in individual mouse mutants with platelet SPD; b) In related studies to analyze by biochemical methods the defect in dense granules and/or in the interaction of dense granules with cytosolic proteins in mutant mice; c) To analyze the abnormal development of granules in megakaryocytes of mutant mice with SPD; d) To determine what percentage of normal cells is needed to correct platelet SPD; e) To determine if bone marrow transplantation, which corrects mutant platelet defects, also corrects known defects in other organs of mutant mice; f) To analyze by hematological and biochemical methods new mouse mutants which are possible models for human bleeding diseases; g) To determine which individual mouse mutants most closely approximate particular classes of human SPD. The specific methods include the use of special mouse mutant stocks with SPD which are genetically identical to the normal parental mouse except for the site of the mutation. These congenic mice enable histocompatible bone marrow engraftment of mutant and normal animals as reciprocal donors and hosts. Primary biochemical abnormalities in the mutants will be sought by high resolution 2-dimensional gel electrophoretic analyses, by cross immunization of normal and mutant mice and by biochemical characterization of platelet dense granules and cytosolic components which interact with dense granules. Altered formation and/or function of dense granules in megakaryocytes will be studied at different developmental stages and after specific incorporation of fluorescent mepacrine and radiolabeled serotonin.